Commit 12a5b529 authored by Al Viro's avatar Al Viro
Browse files

fix copy_tree() regression 



Since 3.14 we had copy_tree() get the shadowing wrong - if we had one
vfsmount shadowing another (i.e. if A is a slave of B, C is mounted
on A/foo, then D got mounted on B/foo creating D' on A/foo shadowed
by C), copy_tree() of A would make a copy of D' shadow the the copy of
C, not the other way around.

It's easy to fix, fortunately - just make sure that mount follows
the one that shadows it in mnt_child as well as in mnt_hash, and when
copy_tree() decides to attach a new mount, check if the last child
it has added to the same parent should be shadowing the new one.
And if it should, just use the same logics commit_tree() has - put the
new mount into the hash and children lists right after the one that
should shadow it.

Cc: stable@vger.kernel.org [3.14 and later]
Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
parent 60bb4529

fs/namespace.c

+24 −7
Original line number Diff line number Diff line
@@ -778,6 +778,20 @@ static void attach_mnt(struct mount *mnt, 
	list_add_tail(&mnt->mnt_child, &parent->mnt_mounts);

}



static void attach_shadowed(struct mount *mnt,

			struct mount *parent,

			struct mount *shadows)

{

	if (shadows) {

		hlist_add_after_rcu(&shadows->mnt_hash, &mnt->mnt_hash);

		list_add(&mnt->mnt_child, &shadows->mnt_child);

	} else {

		hlist_add_head_rcu(&mnt->mnt_hash,

				m_hash(&parent->mnt, mnt->mnt_mountpoint));

		list_add_tail(&mnt->mnt_child, &parent->mnt_mounts);

	}

}



/*

 * vfsmount lock must be held for write

 */
@@ -796,12 +810,7 @@ static void commit_tree(struct mount *mnt, struct mount *shadows) 


	list_splice(&head, n->list.prev);



	if (shadows)

		hlist_add_after_rcu(&shadows->mnt_hash, &mnt->mnt_hash);

	else

		hlist_add_head_rcu(&mnt->mnt_hash,

				m_hash(&parent->mnt, mnt->mnt_mountpoint));

	list_add_tail(&mnt->mnt_child, &parent->mnt_mounts);

	attach_shadowed(mnt, parent, shadows);

	touch_mnt_namespace(n);

}
@@ -1474,6 +1483,7 @@ struct mount *copy_tree(struct mount *mnt, struct dentry *dentry, 
			continue;



		for (s = r; s; s = next_mnt(s, r)) {

			struct mount *t = NULL;

			if (!(flag & CL_COPY_UNBINDABLE) &&

			    IS_MNT_UNBINDABLE(s)) {

				s = skip_mnt_tree(s);
@@ -1495,7 +1505,14 @@ struct mount *copy_tree(struct mount *mnt, struct dentry *dentry, 
				goto out;

			lock_mount_hash();

			list_add_tail(&q->mnt_list, &res->mnt_list);

			attach_mnt(q, parent, p->mnt_mp);

			mnt_set_mountpoint(parent, p->mnt_mp, q);

			if (!list_empty(&parent->mnt_mounts)) {

				t = list_last_entry(&parent->mnt_mounts,

					struct mount, mnt_child);

				if (t->mnt_mp != p->mnt_mp)

					t = NULL;

			}

			attach_shadowed(q, parent, t);

			unlock_mount_hash();

		}

	}

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